Pollen Analysis and Honey Character

Pollen analysis (melissopalynology) is the method of identifying and counting the pollen grains in honey under a microscope to determine which plants and which region the honey came from. As a bee collects nectar it inevitably carries pollen too, and this pollen remains in the honey; so every honey carries the traces of its origin. This page covers how the analysis is done, the definition of monofloral honey, the properties that determine a honey's character, the colours of pollen loads and how the beekeeper can back up their claims.

What is melissopalynology, and what does it tell you?

The pollen grain of each plant species has its own characteristic size, shape, number of apertures (pores and furrows) and surface ornamentation. An expert observer identifies the pollen grains separated from honey with the help of reference collections. The analysis answers the following questions:

• Botanical origin: Which plants did the honey come from; is it monofloral or multifloral?
• Geographical origin: The plant mix typical of a region forms a fingerprint; pollen of endemic species points to the locality.
• Honeydew share: Fungal spores, algae and other honeydew elements indicate honeydew honey.
• Inconsistency: A pollen spectrum that does not match the origin stated on the label, or is unexpected.

How is pollen analysis of honey carried out?

1. Sample preparation: The honey is stirred thoroughly to make it homogeneous; a set amount (usually 10 g) is dissolved in water.
2. Centrifugation: The solution is centrifuged; pollen and other solid particles collect at the bottom as sediment.
3. Slide: The sediment is placed on a microscope slide, stained if necessary and covered with a cover slip.
4. Identification and counting: Under a light microscope, usually several hundred pollen grains (at least 300–500 in most methods) are identified and the percentage of each species is calculated.
5. Evaluation: The pollen percentages are interpreted together with colour, taste, aroma and physicochemical measurements.

Some laboratories also calculate the total number of pollen grains in 10 g of honey; this value helps to distinguish honeys low in pollen (e.g. lavender, citrus) from honeys rich in pollen (e.g. chestnut).

How is monofloral honey defined?

According to the classification established in the literature, the pollen in honey is divided into four groups by frequency:

As a general rule, if a plant's pollen is predominant, the honey may be named after that plant. But plants differ greatly in pollen production:

• Under-represented plants: Plants such as citrus, lavender, black locust, sage, rosemary and lime give plenty of nectar but leave little pollen in honey. For these, much lower percentages (e.g. around 10–20%) may be considered sufficient for a monofloral honey.
• Over-represented plants: The pollen of plants such as chestnut and eucalyptus is very abundant in honey. For these, very high percentages (e.g. 70–90%) are required.

Threshold values vary with national legislation and honey type. The key point is this: a monofloral honey is not decided on pollen percentage alone; colour, aroma, taste, electrical conductivity and sugar profile must also match that honey type.

What determines a honey's character?

• Colour: Ranges from water-white to dark brown; depends on the plant and on minerals.
• Crystallisation: Honeys rich in glucose (sunflower, oilseed rape, cotton) crystallise quickly; honeys rich in fructose (acacia, chestnut) crystallise slowly.
• Electrical conductivity: Reflects mineral content. It is generally low in blossom honeys and high in honeydew honeys and chestnut honey; international standards set 0.8 mS/cm or more for honeydew honey and chestnut honey.
• Taste and aroma: Plant-specific volatile compounds; assessed by trained panellists in sensory analysis.

How is pollen analysis interpreted in honeydew honey?

Honeydew honeys such as pine and oak honey contain little nectar-derived pollen. In these honeys, honeydew elements (fungal spores, fungal hyphae, algae) are counted instead of pollen and their ratio to pollen is calculated. A high ratio supports honeydew honey. In pine honey, air-sac pine pollen blown in by the wind from nearby pines may also be seen; but what really shows the origin of pine honey is the honeydew elements together with high electrical conductivity and a suitable sugar profile.

Which plant does a pollen load colour indicate?

The colour of the pollen loads (pollen pellets) on the legs of bees arriving at the hive entrance is a good clue to which plants are being worked at the time. The colours below are common observations; but the same colour can occur in many plants, and colour changes with moisture and light. A definite identification can only be made with a microscope.

What are the limits of pollen analysis?

• Pollen percentage does not directly reflect nectar share: That is why under- and over-represented plants are assessed by separate criteria.
• Wind and mixing inside the hive: Pollen of plants the bee never visited can get into the honey from the air, or from bee bread in the comb during extraction.
• It requires expertise: Telling apart species of the same family takes experience and a good reference collection.
• Honeydew honey contains little pollen: Different criteria are used.

For this reason, in serious assessments pollen analysis is not used on its own but together with sensory and physicochemical analyses.

Why does over-filtering erase a honey's origin?

Very fine filtering also removes the pollen grains from honey. The honey becomes visually clear, but the trace of its origin is erased; in pollen-free honey, botanical and geographical origin cannot be proven. That is why removing pollen is viewed with suspicion in much legislation and by buyers. The practical conclusion for the beekeeper: coarse straining (a sieve that catches beeswax and bee parts) is enough.

Other honey analysis methods

• Stable isotope analysis: Reveals certain added sugar syrups.
• NMR profiling: Produces a fingerprint of the composition; used to assess both adulteration and origin.
• Physicochemical measurements: Moisture, electrical conductivity, sugar profile, HMF, diastase, colour and acidity.
• Sensory analysis: Assessment of colour, aroma, taste and texture by trained panellists.

What should the beekeeper do?

1. Harvest separately: A claim of monofloral honey can only be defended by extracting separately by period and apiary.
2. Keep records: Which apiary, which period, which plants were in flower, what the hive scale showed.
3. Strain coarsely: Preserve the pollen.
4. Get it analysed: For products carrying commercial claims, have pollen and physicochemical analyses done at an accredited laboratory, and compare the result with your label claim.